It has for some time been common practice to employ both reflective and non-reflective roadway markers adhered to the roadway surface to delineate traffic lanes and other traffic flow patterns. Because such road markers are disposed directly upon the road surface they are subjected to frequent direct impacts from the tires of vehicular traffic, necessitating that such road markers be constructed of high strength, impact resistance material. This criteria has been typically met by utilizing road marker bodies of ceramic or rigid plastic construction, often filled with epoxy resins or similar materials. Such an approach to road marker construction is exemplified by U.S. Pat. No. 3,392,639. Such rigid road marker bodies have had several disadvantages, most notably a tendency to fracture upon repeated impact by vehicular traffic. Such road marker bodies may fracture into several pieces and lose adhesion to the road surface, creating a risk of serious damage or injury if such pieces are thrown by the wheels of passing vehicles.
Another approach which has been attempted in the prior art has been construction of road marker bodies of a soft rubber or rubber-like material, as exemplified by U.S. Pat. No. 3,693,511, in an effort to alleviate the disadvantages associated with hard, rigid road marker bodies. While such an approach is effective in avoiding the problems of road marker body fracture, soft rubber or rubber-like road marker bodies are themselves subject to certain disadvantages. Excessively soft and flexible read marker bodies are subject to deformation leading to release of retroreflector elements from such bodies, with corresponding loss of road marker function. In addition, such materials may suffer accelerated deterioration when exposed to the effects of intense sunlight and of wide ranges of cyclic variation in ambient temperature.
In order to provide a retroreflextive road marker readily visible during periods of darkness it has been common practice to incorporate one or more reflective elements and glass or plastic lenses into the road marker body. Both separated reflective elements and lenses and unitary reflector-lens combinations have been used in the prior art, as illustrated by U.S. Pat. No. 3,971,623 and U.S. Pat. No. 3,392,639, respectively. In many situations it is common to utilize reflective elements of different colors, and in some instances to utilize different colors on opposite sides of the same road marker. It has also been common to utilize road marker bodies of differing colors. Most road markers in the prior art have the retroreflective elements incorporated into the road marker body during construction, requiring the maintenance of relatively large inventories of road markers of the various combinations used.
In addition to this disadvantage, road markers in common use have enjoyed relative short effective life spans due to either failure of the road marker body or, more typically, deterioration of reflective qualities resulting from incursion of water and other contaminants, the effects of sunlight, and abrasion of the outer lens surface from vehicular impact. These problems have necessitated frequent removal of deteriorated road markers and their replacement with new road markers, an expensive and labor intensive process.
From the foregoing, it will be apparent that there has been a need for a road marker system which alleviates the problems and disadvantages of maintenance of large inventories of road markers of differing types, of short effective life span, and of the labor intensive nature of road marker installation.